31 Hygro-mechanical Modelling of Wood and Glutin-based Bond Lines of Wooden Cultural Heritage Objects 275 Fig. 31.2 Clavichord: (a) original instrument and discretised FE-model; (b) two discretised cross-sections of the side wall and simulated moisture intervals m(x,t), with and without shellac coating at alternating climate (30%/80%RH, period τ =2weeks) Exemplarily, the results of internal wood moisture distributions in two cross sections of a side wall of the clavichord are shown in Fig. 31.2. Especially in case of unvarnished surfaces the barrier effect of the bond lines is visible. The large moisture gradient leads to internal hygro-expansional constraints at the adhesive layer and might provoke cracks around the bond line. 31.4 Conclusion and Outlook The new bond line model enables to consider the influence of adhesive layers on the fracture behaviour and the resistance on moisture transport within structural analysis of wooden music instruments. In a first step, the long-term behaviour under consideration of visco-elastic and mechano-sorptive creep [12, 13] is not considered, but will be investigated in the recent research. Moreover, further experimental research on hygro-mechanical fracture behaviour and moisture transport in all members of the investigated structures are required to enhance the accuracy of the simulation results. Keeping in mind that every model is limited, simulation results can help conservators to evaluate constructions, detect overloaded structural members in a non-destructive way and with that develop conservation measures and define climate conditions. Acknowledgement The authors would like to acknowledge the cooperation with the Institute for Building Materials (IfB, ETH, Zurich) and the Stiftung Händel-Haus Halle, and the financial support of their research by the German Research Foundation under grant KA 1163/25. References 1. Bathe, K.-J.: Finite Element Procedure. Prentice Hall, Upper Saddle River, NJ (1996) 2. Resch, E., Kaliske, M.: Three-dimensional numerical analyses of load-bearing behavior and failure of multiple double-shear dowel-type connections in timber engineering. Comput. Struct. 88, 165–177 (2010) 3. Saft, S., Kaliske, M.: Numerical simulation of the ductile failure of mechanically and moisture loaded wooden structures. Comput. Struct. 89, 2460–2470 (2011) 4. Bodig, J., Jayne, B.A.: Mechanics of Wood and Wood Composites. Krieger Publishing, Malabar (1993) 5. Schmidt, J., Kaliske, M.: Simulation of cracks in wood using a coupled material model for interface elements. Holzforschung. 61, 382–389 (2007) 6. Konopka, D., Kaliske, M.: Transient multi-Fickian hygro-mechanical analysis of wood. Comput. Struct. 197, 12–27 (2018) 7. Konopka, D., Gebhardt, C., Kaliske, M.: Numerical modelling of wooden structures. J. Cult. Herit. 27S, S93–S102 (2017) 8. Reichel, S.: Modellierung und Simulation hygro-mechanisch beanspruchter Strukturen aus Holz im Kurz- und Langzeitbereich. PhD Thesis, Technische Universität Dresden (2015)
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